The present invention relates to a method of alkylating compounds, in particular aromatic compounds, with the use of zeolites as catalysts.
The production of aromatic compounds containing cyclic alkyl groups by the use of aluminum halides is known, for instance the synthesis of mono- or dicyclohexylnaphthalenes with AlCl.sub.3, such reactions being described in particular in the following articles:
D. Bodroux, Annales de Chimie 1929, (10) 11, 535;
Charles C. price, J. Am. Chem. Soc, 1943, 65, 439;
E. S. Pokrovskaya, J. Gen. Chem. (USSR), 1939, 9, 1953.
This method leads to a low yield and an absence of selectivity and, furthermore, it is not economical.
Patents or patent applications DE-C-638 756, DE-A 2 208 363, U.S. Pat. No. 2,229,018, and U.S. Pat. No. 3,736,106 describe the alkylation of aromatic compounds by olefins, for instance cyclic olefins, in the presence of catalysts which are clays, for instance montmorillonite, kaolin, hydrosilicates and bleaching earths. These methods are not selective.
U.S. Pat. Nos. 2,904,607, 3,641,177, 4,393,262, DE-A-3 334 084, EP-A-280 055, J. Catal. 1986, 101, page 273 describe the alkylation of aromatic products using zeolites as catalysts, with linear alkylation agents such as, for example, olefins having 2 to 4 carbon atoms or methanol. These documents do not describe the alkylation of aromatic products with cyclic alkyl groups.
Patent Application DE-A-1 934 426 describes a continuous method of preparing alkylated aromatic compounds. That application cites numerous catalysts of zeolite type, for instance natural zeolites, such as gmelinite, dachiardite, faujasite, heulandite and mordenite or synthetic zeolites, such as omega L and Y zeolites. That application also mentions numerous aromatic compounds and a large variety of alkylation agents. This method is carried out in two steps. In a first step, the alkylation is effected with an alkylation agent in the presence of zeolites suspended in the liquid medium. The alkylation is not selective, and a mixture of mono- and polyalkylaromatics is obtained. In order to remedy this absence of selectivity, in a second step the reaction medium obtained from the first step is contacted with a zeolite, without a suspension and without an alkylating agent, so as to effect a transalkylation. Despite this second step, the overall selectivity at the end of these two steps remains low.
U.S. Pat. No. 4,230,894 describes the nonselective alkylation of benzene or alkylbenzene in order to obtain a mixture of isomers which is contacted with a zeolite so as to crack or selectively transalkylate the 1,4-dialkylbenzene isomer in order to enrich the mixture with 1,3-dialkylbenzene isomer.
Patent Application PCT/CH 90/00178 incorporated here by reference describes a method of cycloalkylating naphthalene with at least one cyclic group, this method being characterized by the following points:
(a) as catalyst, there is used at least one zeolite of faujasite structure having pore openings of more than 6.7 .ANG., the silica/alumina weight ratio of this zeolite being greater than 2.5, and its residual concentration in alkaline ion(s) being less than 3% in weight.
(b) the reaction is carried out batch-wise in heterogenous liquid/solid phase at a temperature of between 20.degree. C. and 250.degree. C. under a pressure of at most 30 bars, the zeolite or zeolites being suspended in the reaction medium;
(c) the alkylating-agent/naphthalene molar ratio is at least equal to 1.